Image heating apparatus

ABSTRACT

An image heating apparatus includes a heating member for heating a toner image on a recording material in a heating nip, a pressing member for forming the heating nip and being in contact with the heating member, an abrading member for abrading a surface of the heating member, a contact-and-separation device for causing contact and separation of the abrading member with respect to the heating member, and a selecting device for selecting, depending on the basis weight of the recording material to be heated by the heating member, whether or not the contact-and-separation means brings the abrading member into contact with the heating member before a recording material is conveyed to the heating nip.

This application is a divisional of U.S. patent application Ser. No.12/470,218, filed May 21, 2009, pending.

FIELD OF THE INVENTION AND RELATED ART

The present invention relates to an image heating apparatus (device)suitably used as an image heat-fixing device to be mounted in an imageforming apparatus, such as a copying machine, a facsimile machine, or aprinter, for forming a toner image on a recording material by anelectrophotographic method, an electrostatic recording method, amagnetic recording method, or the like.

As a heating-type image fixing device in an image forming apparatus ofan electrophotographic type, a fixing device for heat-fixing the tonerimage, in a fixing nip in which a fixing member and a pressing membercontact each other, has been used conventionally.

However, a surface layer of the fixing member suffers the problem thatthe layer is gradually roughened due to attack by passing sheets or dueto contamination with paper powder or offset toner, for example.Particularly, when a large number of sheets of the recording material iscaused to pass through a certain position of the fixing member, thedegree of roughening of a surface layer of a fixing roller (member) isdifferent among a sheet passing area, a non-sheet-passing area, and apaper (sheet) edge portion at a boundary between the sheet passing areaand the non-sheet-passing area. Further, when a separation claw (forseparating the recording material, having passed through the fixing nip,from the fixing member) contacts the surface of the fixing member, asurface roughness in a contact area, in which the separation clawcontacts the fixing roller and that in a non-contact area, in which theseparation claw does not contact the fixing roller, are different fromeach other.

When the fixing member surface is roughened, a surface state of thefixing member is transferred onto the toner image surface. When thesurface state of the fixing member is different, a difference in surfacestate correspondingly occurs on the toner image, with the result thatuneven glossiness occurs.

Japanese Laid-Open Application (JP-A) 2008-40365 discloses aconstitution for solving the above-described problem. In thisconstitution, the entire area of the fixing member (the sheet passingarea, the non-sheet-passing area, and the sheet edge portion) isroughened so as to provide fine traces of abrasion by a rougheningmember having a surface layer uniformly provided with abrasive grains(#1000 to #4000). As a result, the difference between pits andprojections at the surface of the fixing member is decreased bysuperposing the fine traces of abrasion deposited on the fixing membersurface, so that low-gloss stripes, occurring at a sheet edge positionon the toner image, and a difference in glossiness between in the sheetpassing area and in the non-sheet-passing area are less conspicuous.Further, the fixing device in the image forming apparatus is constitutedso that the roughening member is movable toward and away from the fixingmember since the roughening member is contaminated with the offset toneror the like on the fixing member when the roughening member alwayscontacts the fixing member. Further, a roughening operation is performedon a regular basis by providing a counter or in a user mode executableby a user, when the user is concerned about uneven image glossiness, byproviding an operating portion with an operation button.

In recent years, the image forming apparatus has been required toprovide a high image quality and high productivity. In order to improveproductivity, it is necessary to increase the conveying speed of therecording material, so that it is desirable that the fixing device iscapable of performing fixation even at a low conveying speed of therecording material.

However, when the fixing speed is increased and a recording material onwhich a solid image is formed is subjected to the fixation operation, itis found that the following problem occurs. That is, when thick paper isused as the recording material and the toner image is fixed on the thickpaper, a sheet edge trace of abrasion, a separation claw trace, or thelike left on the fixing roller surface is conspicuous on the toner imageas the uneven glossiness.

A principal of the occurrence of the uneven glossiness on the tonerimage due to the sheet edge trace of abrasion, the separation clawtrace, or the like left on the fixing roller surface in the cases of thehigh fixing speed and the use of the thick paper as the recordingmaterial will be described.

First, the relationship between the toner melting state and ease of thetransfer of a surface shape of the fixing roller onto the toner image onthe recording material (hereinafter referred to as a surface transferproperty) will be described. The surface transfer property of the tonerimage (an output product) is largely affected by the smoothness of therecording material surface, the amount of the toner, and the tonermelting state.

In the case where the toner amount is small, the surface transferproperty is higher with lower smoothness of the recording materialsurface. This is because the glossiness of the toner is liable to beaffected by the smoothness of the recording material surface.

As shown in FIG. 13( a), in the case where the toner amount is small,the toner image glossiness is liable to be affected by the smoothness ofthe recording material surface. However, as shown in FIG. 13( b), whenthe toner amount is increased, pits and projections of the recordingmaterial surface are filed with the toner. In this case, the toner imagesurface is less affected by the uneven recording material surface.

Therefore, as shown in FIG. 13( c), under the condition that the toneris sufficiently melted, the surface smoothness of the toner image afterthe fixation is increased with an increasing toner amount, thusresulting in a surface transfer property (surface transferability).

When the case of the low fixing speed and the case of the high fixingspeed are compared by applying unfixed toner onto the surface of thethick paper as the recording material, the surface transfer property ofthe case of the high fixing speed is higher than that of the case of thelow fixing speed. Further, when the case where the unfixed toner isapplied onto the thick paper and the case where the unfixed toner isapplied onto thin paper are compared at the same fixing speed, thesurface transfer property of the case where the unfixed toner is appliedonto the thick paper is higher than that in the case where the unfixedtoner is applied onto the thin paper.

As a result of observation of an output product through a lasermicroscope (“VK8000 series”, mfd. by KEYENCE CORP.) with respect tothese phenomena, it has been found that the toner melting state ischanged as described below. Therefore, the change in toner melting statewill be described with reference to schematic views. FIGS. 14( a) to14(d) are schematic views showing a toner melting process in the case ofthe low surface transfer property. Further, FIGS. 15( a) to 15(d) areschematic views showing the toner melting process in the case of thehigh surface transfer property.

FIG. 14( a) is the schematic view showing a state of the unfixed toner,FIG. 14( b) is en enlarged view of FIG. 14( a), FIG. 14( c) is aschematic view showing a state in which the toner is changed from thestate of FIG. 14( b) to a melted state, and FIG. 14( d) is schematicview showing a state of the toner image surface on the recordingmaterial in the case where the unfixed toner is melt-fixed.

Further, FIG. 15( a) is the schematic view showing a state of theunfixed toner, FIG. 15( b) is en enlarged view of FIG. 15( a), FIG. 15(c) is a schematic view showing a state in which the toner is changedfrom the state of FIG. 15( b) to a melted state, and FIG. 15( d) isschematic view showing a state of the toner image surface on therecording material in the case where the unfixed toner is melt-fixed.

As shown in FIG. 14( d), in the case where a certain amount of toner isuniformly melted, an upper layer-side toner and a lower layer-side tonerfollow the surface of the recording material, so that the toner imagesurface is also liable to be affected by the uneven recording materialsurface. Therefore, the resultant surface toner property is low.

As shown in FIG. 15( d), in the case where the lower layer-side toner ofthe toner image is less liable to be melted, only the toner portionclose to the surface of the toner image is melted, so that the tonerimage surface is less liable to be affected by the uneven recordingmaterial surface. As a result, the surface transfer property of thetoner image is high.

As described above, in the case where the conveying speed of therecording material is high, the lower layer-side toner of the tonerimage is not sufficiently heated. As a result, the toner melting stateis the state shown in FIG. 15( d), so that the surface transfer propertyof the toner image is high.

Further, in the case of the thin paper used as the recording materialhaving a small thermal capacity, heat of the toner is less liable to betaken by the recording material and further the heat is liable toconduct from the back side of the paper, so that the lower layer-sidetoner is also heated sufficiently. As a result, the toner melting stateis liable to be changed to the state of FIG. 14( d). On the other hand,in the case of the thick paper used as the recording material having alarge thermal capacity, the heat of the toner is liable to be taken bythe recording material and further the heat is less liable to conductfrom the back side of the paper, so that the toner melting state isliable to be changed to the state of FIG. 15( d).

Thus, when the sheet edge trace of abrasion or the separation claw traceis present on the fixing roller surface, in the toner melting state asshown in the schematic view of FIG. 15( d), the influence of the unevenrecording material surface is less liable to come to the surface of thetoner image. Therefore, the surface smoothness of the toner image afterimage fixation is high. Further, with higher smoothness, the separationclaw trace is more conspicuous. Therefore, when the thick paper isintended to be fixed in the high fixing speed state, the sheet edgetrace of abrasion and the separation claw trace are conspicuous asuneven glossiness of the toner image.

When the roughening operation is always performed by the rougheningmember disclosed in JP-A 2008-40365, the surface of the rougheningmember clogs, so that the lifetime of the roughening member isshortened.

SUMMARY OF THE INVENTION

A principal object of the present invention is to solve the problem,that damage of a fixing member surface is transferred onto a toner imageto cause uneven glossiness on the toner image after fixation, whileavoiding a shortened lifetime of the roughening surface.

Another object of the present invention is to provide an image heatingapparatus solving this problem.

According to an aspect of the present invention, there is provided animage heating apparatus comprising:

a heating member for heating a toner image on a recording material in aheating nip;

a pressing member for forming the heating nip in contact with theheating member;

an abrading member for abrading a surface of the heating member;

contact-and-separation means for permitting contact and separation ofthe abrading member with respect to the heating member; and

selecting means for selecting, depending on the weight of the recordingmaterial to be heated by the heating member, whether or not thecontact-and-separation means brings the abrading member into contactwith the heating member before a recording material is conveyed to theheating nip.

These and other objects, features and advantages of the presentinvention will become more apparent upon a consideration of thefollowing description of the preferred embodiments of the presentinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic structural view of an embodiment of an imageforming apparatus.

FIG. 2 is an enlarged cross-sectional view of a fixing device ofEmbodiment 1.

FIG. 3 is a perspective view of a principal portion of the fixingdevice.

FIG. 4 is a perspective view showing a mounting and demounting mechanismof a roughening roller with respect to a fixing roller.

FIG. 5 is a block diagram of a control system.

FIG. 6 is a schematic view for illustrating the roughening roller.

FIG. 7 is an enlarged cross-sectional view of the fixing device in astate in which an upper separation claw is separated from the fixingroller.

FIG. 8 is a top plan view showing positions of the fixing roller and theseparation claw.

FIG. 9 is a plan view of an operating display portion.

FIG. 10 is a flow chart for explaining an operation in Embodiment 1.

FIG. 11 is an enlarged cross-sectional view of a fixing device ofEmbodiment 2.

FIG. 12 is a flow chart for explaining an operation in Embodiment 2.

FIGS. 13( a) to 13(c), FIGS. 14( a) to 14(d), and FIGS. 15( a) to 15(d)are schematic views for illustrating a surface transfer property.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinbelow, the present invention will be described more specificallybased on embodiments. Incidentally, these embodiments are preferredembodiments of the present invention but the present invention is notlimited thereto.

Embodiment 1

(1) Image Forming Apparatus

FIG. 1 is a schematic structural view of an embodiment of an imageforming apparatus in which a heating apparatus (device) according to thepresent invention is mounted as a fixing device. This image formingapparatus is a full-color laser beam printer of an electrophotographictype wherein an image corresponding to electrical image informationinputted from a host apparatus C, such as a personal computer or animage reader, to a controller (control means: CPU) A is formed on arecording material (transfer paper) S and is outputted. The controller Asends and receives various pieces of the electrical image informationbetween the controller A and the host apparatus C or an operatingdisplay portion (operating portion) B and effects centralized control ofan image forming operation of the image forming apparatus in accordancewith a predetermined control program or a reference table.

In the apparatus, first to fourth image forming stations P (Pa, Pb, Pcand Pd) are provided in parallel and form toner images different incolor through an electrophotographic process including latent imageformation and development.

Each image forming station P is provided with a dedicated image bearingmember, i.e., an electrophotographic photosensitive drum (1 a, 1 b, 1 cor 1 d) in this embodiment. Each photosensitive drum is rotationallydriven in a counterclockwise direction indicated by an arrow at apredetermined speed, so that an associated color toner image is formedthereon. Adjacent to the respective photosensitive drums 1 a, 1 b, 1 cor 1 d, an intermediary transfer belt 8 as an intermediary transferapparatus is provided. The respective color toner images formed on therespective photosensitive drums 1 a, 1 b, 1 c or 1 d areprimary-transferred onto the intermediary transfer belt 8 in asuperposition manner and then are transferred onto the recordingmaterial at a secondary transfer portion. The recording material ontowhich the toner images are transferred is introduced into a fixingdevice 13 and is subjected to a toner image fixing process under theapplication of heat and pressure. Thereafter, the recording material isdischarged on a sheet discharge tray 17 located outside the apparatus asan image-formed product (a full-color print).

At an outer peripheral portion of each of the photosensitive drums 1 a,1 b, 1 c or 1 d, a drum charger (2 a, 2 b, 2 c or 2 d), a developingdevice (4 a, 4 b, 4 c or 4 d), a primary transfer charger (5 a, 5 b, 5 cor 5 d), and a drum cleaner (6 a, 6 b, 6 c or 6 d) are provided. Eachdrum charger 2 a, 2 b, 2 c, 2 d electrically charges the peripheralsurface of its respective photosensitive drum 1 a, 1 b, 1 c, or 1 duniformly to a predetermined polarity and a predetermined potential.Above each of the photosensitive drums 1 a, 1 b, 1 c or 1 d, acorresponding laser scanner (3 a, 3 b, 3 c and 3 d) is provided. Each ofthe laser scanners 3 a, 3 b, 3 c, 3 d includes a light source device, apolygon minor, an fθ lens, and the like although these devices areomitted from illustration. Laser light emitted from the light sourcedevice of each laser scanner is used for scanning by rotating thepolygon minor and beams of the scanning light are deflected by areflection minor and are focused on a generating line on thecorresponding photosensitive drum 1 a, 1 b, 1 c or 1 d to effect lightexposure of the corresponding photosensitive drum surface. By thisscanning exposure to the laser beam, the surface of each photosensitivedrum 1 a, 1 b, 1 c or 1 d electrically charged by its respective drumcharger 2 a, 2 b, 2 c, 2 d, has formed thereon an electrostatic latentimage corresponding to an image signal.

In the developing devices 4 a, 4 b, 4 c and 4 d, as developers, colortoners of yellow, magenta, cyan, and black are contained, respectively,in a predetermined amount. Into each of the developing devices 4 a, 4 b,4 c, 4 d, associated toner is appropriately supplied from associatedsupplying devices (7 a, 7 b, 7 c and 7 d). The respective developingdevices 4 a, 4 b, 4 c, 4 d develop latent images on the associatedphotosensitive drums 1 a, 1 b, 1 c, 1 d into visualized images of yellowtoner image, a magenta toner image, a cyan toner image, and a blocktoner image, respectively.

The intermediary transfer belt 8 is stretched around a driving roller 9,a secondary transfer opposite roller 10, and a tension roller 11 and isrotationally driven in a clockwise direction indicated by an arrow atthe same peripheral speed as that of the respective photosensitive drums1 a, 1 b, 1 c or 1 d.

The yellow toner image of a first color formed and carried on thephotosensitive drum 1 a of the first image forming station Pa isintermediary-transferred onto the intermediary transfer belt 8 duringpassing thereof through a nip (primary transfer portion) between thephotosensitive drum 1 a and the intermediary transfer belt 8. That is,by nip pressure and an electric field formed by a primary transfer biasapplied to the primary transfer charger 5 a, the yellow toner image isintermediary-transferred onto the outer peripheral surface of theintermediary transfer belt 8.

Thereafter, in a similar manner, the magenta toner image of a secondcolor for the second image forming station Pb, the cyan toner image of athird color for the third image forming station Pc, and the black tonerimage of a fourth color for the fourth image forming station Pd aretransferred onto the intermediary transfer belt 8 in the superpositionmanner. As a result, on the intermediary transfer belt 8, unfixedsynthetic color toner images corresponding to the color imageinformation inputted from the host device C to the controller A areformed.

The surface of each photosensitive drum 1 a, 1 b, 1 c, 1 d after beingsubjected to the primary transfer of the toner image onto theintermediary transfer belt 8 is subjected to removal of primary transferresidual toner (cleaning) by its respective drum cleaner 6 a, 6 b, 6 c,6 d and prepares for a next latent image formation and subsequent steps.

Against the secondary transfer opposite roller 10, the intermediarytransfer belt 8 is pressed by a secondary transfer roller 12. Thesecondary transfer roller 12 is supplied with bearings and extendsparallel with the secondary transfer opposite roller 10 so as to contactthe intermediary transfer belt 8. A nip between the intermediarytransfer belt 8 and the secondary transfer roller 12 is a secondarytransfer portion. To the secondary transfer roller 12, a predeterminedsecondary transfer bias is applied with a predetermined control timing.

The transfer of the synthetic color toner images, transferred onto theintermediary transfer belt 8 in a superposition manner, onto therecording material S is performed by introducing the recording materialS into the secondary transfer portion. That is, one of sheets of therecording material S is separated and fed from a first or second sheetfeeding cassette 19 a or 19 b with a predetermined control timing by anoperation of a sheet feeding mechanism. The recording material S isconveyed through a sheet path 20 and passes through a registrationroller 21 and a pre-transfer guide 22 to be conveyed to the secondarytransfer portion with a predetermined control timing and at the sametime, a secondary transfer bias is applied to the secondary transferroller 12. By this secondary transfer bias, the synthetic color tonerimages are collectively transferred from the intermediary transfer belt8 onto the recording material S.

Secondary transfer residual toner and other foreign matter which remainon the intermediary transfer belt 8 are wiped with a cleaning web(nonwoven fabric) of a belt cleaner 18.

The recording material S subjected to the secondary transfer of theunfixed synthetic color toner images at the secondary transfer portionis separated from the intermediary transfer belt 8 and introduced intothe fixing device 13 to be subjected to the toner image fixing processunder the application of heat and pressure. Then, the recording materialS comes out of the fixing device 13 and is conveyed by a conveyingroller pair 14 and thereafter passes through an upper side of a flapper15 and is discharged on the sheet discharge tray 17 located outside theapparatus (the case of a one-side image forming mode).

In the case of a two-side image forming mode, the recording material S,coming out of the fixing device, which has already been subjected to theone-side image formation (image formation on a front surface) isconveyed by the conveying roller pair 14 and is guided into a reversepath 23 by the flapper which has been changed in attitude. Then, therecording material S is reversed by a reversing roller (a switchbackroller) 24 to be guided into a two-side path 25 and is introduced intothe secondary transfer portion again through the sheet path 20, theregistration roller 21, and the pre-transfer guide 22. As a result, therecording material S is subjected to the secondary transfer of the tonerimages on a second (back) surface of the recording material S. Then, therecording material S is separated from the intermediary transfer belt 8and is introduced into the fixing device 13 again to be subjected to thetoner image fixing process with respect to the second surface. Theflapper 15 is changed in attitude to its original attitude during thetwo-side image formation on the recording material S. As a result, thetwo-side image-formed recording material S coming out of the fixingdevice 13 is conveyed by the conveying roller pair 14 and passes throughthe upper side of the flapper 15, thus being discharged on the sheetdischarge tray 17 located outside the apparatus by the sheet dischargeroller 16.

(2) Fixing Device 13

FIG. 2 is an enlarged cross-sectional view of the fixing device 13, andFIG. 3 is a perspective view of a principal portion of the fixing device13. FIG. 4 is a schematic view of a mounting and demounting mechanism ofa roughening roller with respect to a fixing roller, and FIG. 5 is ablock diagram of a control system.

The fixing device 13 is an image heating apparatus of a heating rollertype and includes a fixing roller 40 and a pressing roller 41 as a pairof rotatable members which contact each other to form a heating nip(fixing nip) for heating the toner images on the recording material.

Herein, a front side of the fixing device 13 refers to an entrance side26 of the recording material S. Left and right sides of the fixingdevice 13 refer to those as seen from the front side of the fixingdevice 13.

In this embodiment, the fixing roller 40 is prepared by forming a 2.0mm-thick silicone rubber layer, as an elastic layer, having a rubberhardness of 20 degrees (JIS-A 1 kg weight) on a core metal consisting ofa hollow pipe of Al having an outer diameter of 66 mm. Further, thesurface of the elastic layer is coated with a 50 μm-thickfluorine-containing resin material layer as a surface parting layer toprepare an elastic roller having an outer diameter of 70 mm The surfaceparting layer is a fluorine-containing resin material tube. Generally,the fluorine-containing resin material tube is constituted by PFA resin(tetrafluoroethylene-perfluoroalkoxyethylene copolymer) PTFE(polytetrafluoroethylene), or the like.

Further, the pressing roller 41 is prepared, similarly as in the case ofthe fixing roller 40, by forming a 2.0 mm-thick silicone rubber layer,as an elastic layer, having a rubber hardness of 20 degrees (JIS-A 1 kgweight) on a core metal consisting of a hollow pipe of Al having anouter diameter of 66 mm. Further, the surface of the elastic layer iscoated with a 50 μm-thick fluorine-containing resin material layer as asurface parting layer to prepare an elastic roller having an outerdiameter of 70 mm.

By combining the above-constituted fixing roller 40 and pressing roller41, the parting property thereof with respect to the toner is furtherenhanced.

The fixing roller 40 and the pressing roller 41 are vertically disposedin parallel and rotatably held by bearings between left and right sideplates (not shown) of a device frame 43. The fixing roller 40 and thepressing roller 41 press-contact each other against the elastic layersthereof with a total pressure of about 1666 N (170 kgf) by a pressingmechanism (not shown). As a result, a nip (fixing nip) N having apredetermined width is formed between the fixing roller 40 and thepressing roller 41 with respect to a recording material conveyancedirection.

On a right end side (driving side) of the core metal of the fixingroller 40, a drive inputting gear 44 is provided concentrically integralwith the fixing roller 40. To this drive inputting gear 44, a drivingforce is transmitted from a driving means M1 to rotationally drive thefixing roller 40 in a clockwise direction indicated by an arrow in FIG.2 at a predetermined speed. The pressing roller 41 is rotated in acounterclockwise direction indicated by an arrow by the rotational driveof the fixing roller 40. In this embodiment, the driving speed of thefixing roller 40 is set so that the conveyance speed of the recordingmaterial 3 is 700 mm/sec.

Into the inside of the core metal of the fixing roller 40 m a halogenheater 42 a as a heating means is inserted and disposed. Further, alsointo the inside of the core metal of the pressing roller 41, a halogenheater 42 b as the heating means is inserted and disposed. To thehalogen heaters 42 a and 42 b, electric power is supplied from electricenergy supplying portions 43 a and 43 b, respectively. As a result, thehalogen heaters 42 a and 42 b generate heat, so that the fixing roller40 and the pressing roller 41 are heated from the insides thereof.Further, thermistors 44 a and 44 b as temperature detection means fordetecting temperatures of the fixing roller 40 and the pressing roller41, respectively, are provided in contact with outer surfaces of thefixing roller 40 and the pressing roller 41.

With respect to the fixing roller 40, a roughening roller (rougheningmember) 93 as an abrading member for abrading the surface of the fixingroller 40 is provided for movement toward and away from the fixingroller 40.

On a recording material exit side of the fixing nip N, an upperseparation claw 34 contactable to the fixing roller 40 and a lowerseparation claw 35 contactable to the pressing roller 41 are swingablyprovided. The upper separation claw 34 and the lower separation claw 35are separation members for separating the recording material from thefixing roller 40 and the pressing roller 41.

The controller A turns on the driving means M1 and the electric energysupplying portions 43 a and 43 b with a predetermined control timing.Into the controller A, temperature detection information of thethermistors 44 a and 44 b (electric information on temperatures of thefixing roller 40 and the pressing roller 41) is inputted. The controllerA controls electric power supplied from the electric energy supplyingportion 43 a to the halogen heater 42 a and electric power supplied fromthe electric energy supplying portion 43 b to the halogen heater 42 b sothat the temperature detection information inputted from the thermistors44 a and 44 b is used to control the electric power supplied to theheaters 42 a and 42 b to set the temperature of the fixing roller 40 andthe pressing roller 41 to a predetermined set temperature (fixingtemperature). In this embodiment, the controller A transfer-controls thefixing roller 40 and the pressing roller 41 so that the transfers of thefixing roller 40 and the pressing roller 41 are increased up to about180° C. as the fixing temperature and are kept at a substantiallyconstant level. In this state, the recording material S carrying theunfixed toner images is introduced from the entrance 26 into the fixingdevice 13 and is guided by an entrance-side guide 26 a to enter thefixing nip N, thus being heated and pressed by being nip-conveyed in thefixing nip N (by a heating operation of the fixing roller 40 and thepressing roller 41). As a result, the unfixed toner images are fixed onthe recording material S as a fixed image. The recording material Shaving passed through the fixing nip N is separated from the fixingroller 40 and the pressing roller 41 by the upper separation claw 34 andthe lower separation claw 35 and is guided by an exit-side guide 26 b,thus coming out of the fixing device 13 to be further conveyed by theconveying roller pair 14.

(3) Roughening Roller 93 and Mounting and Demounting Mechanism

FIG. 6 is a schematic view for illustrating a structure of theroughening roller 93. In this embodiment, the roughening roller 93 isprepared by hermetically bonding abrasive grains to an outer peripheralsurface of a core metal 97, of SUS having a diameter of 12 mm, throughan adhesive layer 98. The abrasive grains 99 have a grain size of #1000to #4000 and have a grain size distribution. The grain size of #1000corresponds to about 16 μm and the grain size of #4000 corresponds toabout 3 μm. The abrasive grains 99 are those of alumina (also commonlycalled “Alundum” or “molundum”). The alumina abrasive grains are widelyused and have a sufficiently higher hardness than that of the fixingroller 40 and have an acute shape, thus being excellent inmachinability.

As the roughening roller 93, those having a surface roughness Rz of 3 μmto 16 μm can be used. Below 3 μm, the fine traces of abrasion are notleft on the fixing roller 40, so that a roughening effect is notachieved. Above 16 μm, large traces of abrasion are excessively left onthe fixing roller 40, so that the traces of abrasion appear as an imageon the recording material.

The surface roughness Rz can be measured by using a surface roughnessmeasuring device (“SE-3400”, mfd. by Kosaka Laboratory Ltd.) under ameasuring condition including a feeding speed of 0.5 mm/sec, a cut offof 0.8 mm, and a measuring length of 2.5 mm.

The roughening roller 93 is disposed substantially in parallel with thefixing roller 40 so as to be movable toward and away from the fixingroller 40. Mounting of the roughening roller 93 to the fixing device 13will be described with reference to FIGS. 3 and 4. In the followingdescription, members corresponding to parenthesized reference symbolsare not visible in the figures due to overlapping with other members.

The roughening roller 93 is supported by being rotatably mounted to apair of left and right supporting members 46 a and 46 b through bearings45 a and 45 b at both end portions thereof. The supporting members 46 aand 46 b are rotatably supported about supporting shafts 47 a and (47b), respectively. Further, on the supporting members 46 a and 46 b,urging springs 48 a and 48 b for rotationally urging the supportingmembers 46 a and 46 b about the supporting shafts 47 a and (47 b), sothat the roughening roller 93 can be moved to contact the fixing roller40, are hooked. The urging springs 48 a and 48 b are locked by fixedspring hooking shafts at other ends. In this embodiment, by these urgingsprings, an urging force of 10 N to 150 N as a total pressure for urgingthe roughening roller 93 against the fixing roller 40 is generated. Theroughening roller 93 is fixed with a gap by longitudinal left and rightE-shaped stopper (snap) rings (62 a) and 62 b so that the rougheningroller 93 does not stretch to the bearings 45 a and 45 b even when theroughening roller 93 is thermally expanded.

Next, a contact-and-separation mechanism for movement of the rougheningroller 93 toward and away from the fixing roller 40 will be described. Apair of left and right retraction arms 52 a and 52 b are rotatablymounted about rotational shafts 53 a and 53 b corresponding to theabove-described supporting members 46 a and 46 b. The retraction arms 52a and 52 b are rotationally urged about the rotational shafts 53 a and53 b by retraction springs 54 a and (54 b) so as to contact thesupporting members 46 a and 46 b at portions 55 a and (55 b). Thesupporting members 46 a and 46 b are configured to be rotationallydriven about the supporting shafts 47 a and (47 b) against the forces ofthe retraction springs 54 a and 54 b by the contact of the retractionarms 52 a and 52 b therewith at the portions 55 a and (55 b). When thesupporting members 46 a and 46 b are rotationally driven by the forcesof the retraction springs 54 a and 54 b, the roughening roller 93 ismoved apart from the fixing roller 40.

At portions 57 a and 57 b, operation arms 56 a and 56 b contact theretraction arms 52 a and 52 b. The operation arms 56 a and 56 b arerotatably more about an arm shaft 58. The arm shaft 58 is rotationallydriven by a driving means M2 through a drive input gear 59 provided atan end (right end) thereof. To the other end (left end) of the arm shaft58, a rotational movement detection flag 60 is attached and aphoto-sensor 61 for detecting a rotational phase of the rotationalmovement detection flag 60 is provided to the flag 60. The controller Acontrols the driving means M2 by the flag 60 and the photosensor 61,thereby controlling rotational phase angles of the operation arms 56 aand 56 b.

When the operation arms 56 a and 56 b press the retraction arms 52 a and52 b at the portions 57 a and 57 b, the retraction arms 52 a and 52 brotate about the rotational shafts 53 a and 53 b against the forces ofthe retraction springs 54 a and (54 b). In interrelation with therotational movement of the retraction arms 52 a and 52 b, the supportingmembers 46 a and 46 b rotationally move about the supporting shafts 47 aand (47 b) by the forces of the urging springs 48 a and 48 b. As aresult, the roughening roller 93 is pressed against the fixing roller 40(a contact operation of the roughening roller 93 with respect to thefixing roller 40).

That is, the rotational phase angles of the operation arms 56 a and 56 bare controlled by the driving means M2 controlled by the controller A,so that the roughening roller 93 is detachably controlled between apress-contact state and a separated state with respect to the fixingroller 40.

The controller A normally controls the driving means M2 so that theoperation arms 56 a and 56 b are held at the rotational phase angles atwhich they do not press the portions 57 a and 57 b of the retractionarms 52 a and 52 b. As a result, the roughening roller 93 is held in theseparated state from the fixing roller 40 by the above-describedmechanism. When the operation arms 56 a and 56 b are held at therotational phase angles at which they press the portions 57 a and 57 bof the retraction arms 52 a and 52 b by controlling the driving means M2by the controller A, the roughening roller 93 is placed in thepress-contact state with respect to the fixing roller 40. In thisembodiment, the contact-and-separation mechanism as acontact-and-separation means for measurement of the roughening roller 93toward and away from the fixing roller 40 is constituted by the drivingmeans M2, the operation arms 56 a and 56 b, the retraction arms 52 a and52 b, the supporting members 46 a and 46 b, and the urging springs 48 aand 48 b.

Next, with reference to FIG. 3, the driving of the roughening roller 93will be described. To a roller shaft of the fixing roller 40 on anon-driving side (left end side), a roughening roller drive transmissiongear 49 is fixedly provided coaxially with the fixing roller 40.Therefore, the gear 49 is rotated integrally with the fixing roller 40.On a left end side of the roughening roller 93, a roughening rollerdrive input gear 50 is provided. A roughening roller driving force istransmitted from the gear 49 to the gear 50 through an idler gear 51. Bythe mediation of the idler gear 51, the roughening roller 93 rotates ina counter direction with respect to the rotation of the fixing roller 40(in a direction opposite from the rotational direction of the fixingroller 40 at their contact portion). In this embodiment, the peripheralspeed of the fixing roller 40 is set at 700 mm/sec and that of theroughening roller 93 is set at 350 mm/sec. By the rotational driving ofthe roughening roller 93 in the counter direction with respect to thefixing roller 40, the relative speed difference between the fixingroller 40 and the roughening roller 93 is set at 1050 mm/sec.

The roughening roller drive input gear 50 is mounted to and demountedfrom (engaged with and disengaged from) the idler gear 51 by themounting and demounting of the roughening roller 93 with respect to thefixing roller 40. When the roughening roller 93 contacts the fixingroller 40, the roughening roller drive input gear 50 engages with theidler gear 51. As a result, the rotation of the gear 49 is transmittedto the gear 50 through the idler gear 51 to rotationally drive theroughening roller 93. When the roughening roller 93 is separated fromthe fixing roller 40, the gear 50 is separated from the idler gear 51and is not engaged with the idler gear 51, so that the driving force isnot transmitted to the roughening roller 93.

(4) Separation Claws 34 and 35 and Mounting and Demounting Mechanism

The structure of the separation claws 34 and 35 will be described withreference to FIG. 2. The upper separation claw 34 is provided so as tocontact the fixing roller 40 and the lower separation claw 35 isprovided so as to contact the pressing roller 41. The recording materialS having passed through the nip N is separated from the fixing roller 40and the pressing roller 41 by the upper separation claw 34 and the lowerseparation claw 35 and comes out of the fixing device 13 to be furtherconveyed by the conveying roller pair 14 shown in FIG. 1.

The upper separation claw 34 will be described more specifically. Theupper separation claw 34 is provided in a plurality of separation clawportions along a longitudinal direction of the fixing roller 40. Theupper separation claw 34 is rotatably supported about the supportingshaft 36 and contacts the fixing roller 40 with a predetermined pressure(=0.049 N (5 gf)) by a spring 37. On a rear end side of the upperseparation claw 34, a wire 39 connected to a solenoid 38 as a drivingmeans, which is to be turned on and off by the controller A, is mounted.When the solenoid 38 is turned on, the upper separation claw 34 ispulled up against the spring 37 on the rear side thereof. As a result,the upper separation claw 34 is rotationally moved about the supportingshaft 36 in a direction in which the upper separation claw 34 is movedapart from the fixing roller 40, so that a front end portion of theupper separation claw 34 is slightly separated from the surface of thefixing roller 40. That is, the upper separation claw 34 is separatedfrom a separation position, in which a separation operation isperformed, by turning on the solenoid 38. The distance between thefixing roller 40 and the front end of the upper separation claw 34 isset at 1 mm to 1.5 mm during heating of the fixing roller 40. This stateis shown in FIG. 7. As the solenoid 38, a latching solenoid is used. Thelatching solenoid is configured so that a current passes through thesolenoid when the solenoid is turned on and off, so that a resultantstate thereof after the current passes through the solenoid can be heldby a magnetic force without the passing of the current.

The solenoid 38 may be provided to each of the separation claws but mayalso perform a mounting and demounting operation of all the separationclaws by a single solenoid 38. As the mounting and demounting mechanismfor the upper separation claw 34, a constitution in which the upperseparation claw 34 is rotationally moved about the supporting shaft 36is described above but it is also possible to employ such a constitutionthat the upper separation claw 34 is slid together with a separationclaw supporting table.

The upper separation claw 34 is appropriately arranged correspondinglyto various sizes of the recording material S (sheet sizes) with respectto the longitudinal direction of the fixing roller 40. FIG. 8 shows anarrangement example of the upper separation claw 34 in the case where arecording material conveyance center is located at a longitudinal centerposition, i.e., in the case of center sheet feeding (center line basisconveyance). Upper separation claws 34 a to 34 f are providedcorrespondingly to an A4-sized recording material and the upperseparation claws 34 b to 34 e are provided correspondingly to a B5-sizedrecording material. Further, the upper separation claw 34 c and 34 d areprovided correspondingly to a B5R-sized recording material and contactthe fixing roller 40 by the springs 37.

The lower separation claw 35 also has the same constitution as that ofthe upper separation claw 34 and is provided in a plurality ofseparation claw portions along a longitudinal direction of the pressingroller 41. That is, the lower separation claw 35 is rotatably supportedabout the supporting shaft 84 and contacts the pressing roller 41 with apredetermined pressure (=0.049 N (5 gf)) by a spring 81. On a rear endside of the lower separation claw 35, a wire 83 connected to a solenoid82 as a driving means which is to be turned on and off by the controllerA is mounted. When the solenoid 82 is turned on, the lower separationclaw 35 is pulled down against the spring 81 on the rear side thereof.As a result, the lower separation claw 35 is rotationally moved aboutthe supporting shaft 84 in a direction in which the lower separationclaw 35 is moved apart from the pressing roller 41, so that a front endportion of the lower separation claw 35 is slightly separated from thesurface of the pressing roller 41. That is, the lower separation claw 35is separated from a separation position, in which a separation operationis performed, by turning on the solenoid 82. A distance between thepressing roller 41 and the front end of the lower separation claw 35 isset at 1 mm to 1.5 mm during heating of the pressing roller 41. Then,when the solenoid 82 is turned off, the lower separation claw 35contacts the pressing roller 41. As the solenoid 82, a latching solenoidis used.

(5) Reason that Roughening Roller 93 and Separation Claw 34 are Required

The reason that the roughening roller 93 is required will be described.When a large number of sheets of the recording material S passes throughthe fixing roller 40 at a certain position, a degree of roughening ofthe fixing roller surface layer varies depending on areas (portions)including the sheet passing area, the non-sheet passing area, and thesheet edge portion in the boundary between the sheet passing area andthe non-sheet passing area.

The surface of the fixing roller 40 including the parting layer of thefluorine-containing resin material or the like as the fixing rollersurface layer is in a mirror-surface state and generally has a surfaceroughness Rz of about 0.1 μm to about 0.3 μm. In the sheet passing area(portion) of the recording material of the fixing roller 40, the fixingroller surface layer is gradually roughened by the attack of fibers,internal and external additives, or the like of the recording material(paper), so that the surface roughness Rz is gradually increased up toabout 1.0 μm.

At the sheet edge portion, due to the presence of flash of papergenerated during cutting of the paper, the attack on the fixing rollersurface layer is large, so that the surface roughness Rz is graduallyincreased up to about 1.0 jam to about 2.0 μm. The flash of paper isliable to be generated, e.g., when a cutting edge is abraded to belowered in sharpness in a cutting step of the paper from a large-sizedsheet.

In the non-sheet passing area (portion), the recording material S doesnot pass through the area, so that the surface roughness Rz isincreased, up to about 1.0 μm, more slowly than that in the sheetpassing area while the fixing roller surface layer contacts the oppositepressing roller 41.

At the separation claw contact portion, the separation claw 34 abradesthe fixing roller surface, so that the surface roughness Rz is notincreased and is about 0.5 μm.

As a result, the surface roughness of the fixing roller 40 aftercontinuous sheet passing is changed in the order of: (sheet edgeportion)>(sheet passing area)>(non-sheet passing area)>(separation clawcontact portion)>(initial state). Therefore, the surface state of thefixing roller 40 varies depending on its longitudinal position.

Further, the surface transferability is high during the fixation on thethick paper, so that a minute surface state of the fixing roller 40 istransferred onto the toner image surface after the fixation. When thesurface state on the fixing roller is different, a difference in surfacestate is correspondingly caused on the toner image, thus resulting in anoccurrence of the uneven glossiness.

Therefore, the fine traces of abrasion are provided in the entire area(the sheet passing area, the non-sheet passing area, and the sheet edgeportion) of the fixing roller surface layer by the roughening roller 93.As a result, the fine traces of abrasion left on the fixing rollersurface layer are superposed to eliminate the difference in the unevensurface state in the surface passing area, the non-sheet passing area,and the sheet edge portion on the fixing roller surface layer, so that anon-uniform low glossiness stripe at the sheet edge portion on the imageand the difference in glossiness between in the sheet passing area andin the non-sheet passing area can be eliminated.

In order to provide the fine traces of abrasion on the fixing rollersurface layer by the roughening roller 93, the rotation of theroughening roller 93 is required to provide a peripheral speeddifference with respect to the rotation of the fixing roller 40. Forthis purpose, in this embodiment, the drive input is made as describedabove so that the roughening roller 93 and the fixing roller 40 providethe relative speed difference of 1050 mm/sec. However, the rougheningeffect can also be obtained even when the relative speed difference V isnot 1050 mm/sec., i.e., when the relative speed difference is given.That is, the relative speed difference is only required to satisfy thefollowing relationship:0 mm/sec<(relative speed difference)<2000 mm/sec.,preferably,0 mm/sec<(relative speed difference)<1500 mm/sec.

However, the relative speed difference and a roughening time are in aproportional relationship, so that when the relative speed difference isset at a small value, the roughening time is required to be set at alarge value. In this embodiment, the roughening time is set at a time inwhich the pressing roller is rotated ten times.

Due to the high surface transfer property, the trace of abrasion and theseparation claw trace left on the fixing roller surface were visualizedon the image in the case where plain paper had the basis weight of 160g/m² or more. Further, in a state of the good surface transfer property,even when the fixing roller 40 is roughened by the roughening roller 93before the fixation, the separation claw trace appears on the image whenthe separation claw 34 contacts the fixing roller 40 during the sheetpassing. That is, the trace of the separation claw 34 is transferredonto the image unless the fixing roller surface is continuouslyroughened by the roughening roller 93. On the other hand, the sheet edgetrace of abrasion occurs at the edge of the paper, so that the sheetedge trace of abrasion does not appear on the image unless the recordingmaterial sheet is changed.

In order to prevent the separation claw trace, the fixing roller 40 maybe roughened continuously by the roughening roller 93 also during thefixing operation. However, a slight amount of the contamination (foreignmatter) such as the offset toner, the paper powder, or the carrier ofthe developer deposited on the fixing roller surface during the fixingoperation can be deposited on the roughening roller surface. When thefixing roller 40 is roughened by the roughening roller 93 on which theforeign matter has been deposited, the surface layer of the fixingroller 40 is damaged, so that an image stripe, such as uneven glossinessor the traces of abrasion, can occur on the image.

The reason that the separation claw 34 is required to contact the fixingroller 40 is as follows. That is, the toner is deposited on the fixingroller surface when the unfixed toner on the recording material iscrushed in the fixing nip, so that the recording material S winds aboutthe fixing roller 40 without being separated from the fixing roller 40.

In the state in which the recording material S winds about the fixingroller 40 without being separated from the fixing roller 40, therecording material S is still nip-conveyed in the fixing nip, so that aseparation force is exerted on the recording material S due toflexibility of the recording material S toward a direction in which therecording material S is separated from the fixing roller 40.

When the separation force by the flexibility of the recording material Sis larger than an adhesion force between the fixing roller 40 and therecording material S, the recording material S is separated from thefixing roller 40 and does not wind about the fixing roller. Theflexibility of the recording material S is affected by the thickness ofthe recording material S, thus being smaller with thinner paper andbeing larger with thicker paper. Therefore, the thin paper is liable towind about the fixing roller 40 and the thick paper is less liable towind about the fixing roller 40. When the recording material S does notwind about the fixing roller 40, it is not necessary to separate therecording material S from the fixing roller 40 by the separation claw34, so that the separation claw 34 can be placed in the separated statefrom the fixing roller surface.

Under the condition in this embodiment, in the case of using therecording material having the basis weight, of 100 g/m² or more, as aweight per unit area, the recording material was conveyable even in thestate in which the separation claw 34 was separated from the fixingroller 40. Therefore, in this embodiment, in order that the separationclaw 34 does not abrade the surface of the fixing roller 40 and that therecording material is separated from the fixing roller 40 withreliability, the separation claw 34 is brought into contact with thefixing roller 40 in the case where the basis weight of the recordingmaterial used is 120 g/m² or less. On the other hand, in the case wherethe basis weight of the recording material used is more than 120 g/m²,the separation claw 34 is configured to be separated from the fixingroller 40.

In this embodiment, in order to prevent the occurrence of the imagestripe due to, for example, uneven glossiness or the traces of abrasiondue to the foreign matter deposited on the surface of the rougheningroller 93, a cleaning member (not shown) for removing the contamination(the foreign matter) such as the toner or the like on the surface of theroughening roller 93 may also be added.

(6) Operation Display Portion B

Next, the operation display portion B for permitting operation of theimage forming apparatus will be described. FIG. 9 is a plan view of theoperation display portion B. The user inputs the basis weight of therecording material to be used through the operation display portion B.

In FIG. 9, a reference numeral 400 represents the copy start key forproviding copy start instructions. A reference numeral 401 represents areset key for returning a current mode to a normal mode. In thisembodiment, the normal mode is set for image formation of“monochromatic/one side/non-clear”. A reference numeral 402 represents aguidance key to be pressed when a guidance function is used. A referencenumeral 403 represents numeric keys for inputting numeric values such asthe pre-set number of sheets and the like. A reference numeral 404represents a clear key for clearing an inputted numeric value. Areference numeral 405 represents a stop key for stopping the copyoperation during continuous copying. A reference numeral 406 representsa liquid crystal display portion of a touch panel type for displayingsettings for various modes and a state of the printer. A referencenumeral 407 represents an interrupt key for making an emergency copy byprocessing the interrupt during the continuous copying operation orduring use as a facsimile machine or a printer. A reference numeral 408represents a personal identification key for managing the number ofsheets copied by individual or division. A reference numeral 409represents a soft switch for turning on and off an electric power sourceof an image forming apparatus main assembly. A reference numeral 410represents function keys to be used when the function of the imageforming apparatus is changed. A reference numeral 411 represents a usermode key for entering a user mode in which the user pre-sets items suchas ON/OFF of auto cassette change and a change in setting time until thecurrent mode is changed to an energy saving mode. By the setting of theuser mode, it is possible to display setting buttons for the user modeon the liquid crystal display portion 406. For example, in FIG. 9,setting of the user mode is made so that a reference numeral 450represents a refreshing mode selection key, a reference numeral 451represents a two-side image forming mode selection key, a referencenumeral 452 represents a full-color image forming mode selection key,and a reference numeral 453 represents a monochromatic color imageforming mode selection key. When the refreshing mode selection key(refreshing button) 450 is pressed, the roughening operation isperformed.

(7) Apparatus Operation Control

The apparatus operation will be described by using a flow chart shown inFIG. 10. First, in the case of performing a printout operation, the userinputs a transfer paper (recording material) condition and the number ofprintout copies to be made through the operation display portion B toset a printout condition. Then, the user turns on the copy start key(printout start switch) 400 to start the printout. Then, the controllerA as a selecting means selects whether or not the above-described movingmeans performs a contact operation of the roughening roller 93 withrespect to the fixing roller 40 in advance of the heating operation (thefixing operation) by the fixing roller 40 and the pressing roller 41,depending on the basis weight of the recording material (the thicknessof the paper) used for the sheet passing. In this embodiment, when theprintout is started, the controller A turns off the separation clawseparation solenoid 38 in the case where the basis weight of therecording material (the thickness of the paper) used for the sheetpassing is not more than a predetermined value (120 g/m² in thisembodiment) on the basis of the user input value. As a result, theseparation claw 34 is placed in the contact state with the fixing roller40 (YES of step S1 and step S2). That is, in the case where the basisweight of the recording material is not more than the above-describedpredetermined value, the separation claw 34 is located at the separationposition in which the separation claw 34 performs the separationoperation when the recording material passes through the fixing nip N.

Then, the controller A starts the sheet passing (step S3) to start theimage formation and also starts the fixing operation in the fixingdevice 13.

The controller A has a counting function for counting the number ofsheets of the recording material S subjected to the fixation in thestate in which the separation claw 34 contacts the fixing roller 40. Inthe case where the sheet passing of 5000 sheets or more (integratednumber of sheets) of the recording material is performed in the contactstate of the separation claw 34, the sheet passing job is interruptedand the roughening operation (refreshing operation) of the fixing roller40 by the roughening roller 93 is started (step S4, YES of step S5, stepS6, and step S7). The roughening operation is performed by the contactoperation of the roughening roller 93 with respect to the fixing roller40 performed by the moving means controlled by the controller A. Theroughening operation is performed under the above-described conditionfor the time period corresponding to 10 times of the rotation of thefixing roller 40 with respect to the roughening roller 93 in thisembodiment. The controller A performs the separation operation of theroughening roller 93 from the fixing roller 40 after the lapse of thetime period. That is, the roughening roller 93 is configured to performthe roughening operation at regular intervals so as not to increase thesurface roughness non-uniformity of the fixing roller 40. When theroughening operation is completed, the sheet passing is resumed (step S2and step S3). When the printout on the set number of sheets is completedin accordance with the above-described routine, the sheet passing iscompleted (NO of step S5 and YES of step S10). When the sheet passing iscompleted, the separation claw separation solenoid 38 is turned on, sothat the separation claw 34 is moved away from the fixing roller 40(step S11).

The controller A as the selecting means performs the rougheningoperation in advance of the heating operation (the fixing operation) bythe fixing roller 40 and the pressing roller 41 in the case where thebasis weight of the recording material S to be fixed is more than thepredetermined value (120 g/m² in this embodiment). That is, theroughening roller 93 is brought into contact with the fixing roller 40by the above-described contact and separation mechanism to perform theroughening operation before the sheet passing (NO of step S1 and stepS8). By performing the roughening operation in the separated state ofthe separation claw 34, the surface state of the fixing roller 40 isuniformized. Further, the separation claw 34 is still separated from thefixing roller 40 after the roughening operation, so that the surfacestate of the fixing roller 40 can be kept at a uniformly roughened stateeven when the sheet passing is performed (step S9). Then, the apparatusstarts the sheet passing to effect the image formation and when theprintout on the set number of sheets is completed, the sheet passing isended and the solenoid is turned on (step S10 and step S11).

With respect to the timing for performing the roughening operation, inorder not to increase the sheet edge traces of abrasion and the surfaceroughness non-uniformity, the roughening operation is performedperiodically by using a counter for each of the recording materialsizes, in addition to the above-described timing.

Further, when the user is concerned about the uneven glossiness on theimage, as the user mode, the constitution in which the fixing roller isuniformly roughened in a stand-by state by providing the operationbutton 450 to the operation display portion B is also employed.

Further, the roughening time is also adjustable by the user.

As described above, the roughening operation of the fixing roller 40 isperformed in advance of the fixing operation when the toner images arefixed on the thin paper having the small basis weight and is notperformed in advance of the fixing operation when the toner images arefixed on the thick paper having the large basis weight. As a result, itwas possible to prevent the traces (of abrasion) from being transferredfrom the surface of the fixing roller 40 onto the toner images on thethin paper and to prolong the lifetime of the roughening roller 93.

Embodiment 2

Embodiment 2 will be described with reference to FIG. 11. In recentyears, an image forming apparatus capable of printing out the recordingmaterial S subjected to two-side printing has been generally used. Forthat reason, in the case where two side images are intended to be fixedon the recording material, the separation claw trace (by the separationclaw 35) left on the surface of the pressing roller 41 is alsotransferred onto the toner images on the thick paper when the thickpaper is passed through the fixing nip at high speed.

For that reason, similarly as in Embodiment 1, a roughening roller 80for movement toward and away from the pressing roller 41 may be providedon the pressing roller 41 side. Further, the lower separation claw 35may also be provided similarly so as to be movable toward and away fromthe pressing roller 41. As the roughening roller 80, a member having thesame constitution as that of the roughening roller 93 for roughening thefixing roller 40 can be used. The roughening roller 80 can be used so asto be pressed against the pressing roller 41 with a total pressure of 10N to 150 N.

Next, the apparatus operation in Embodiment 2 will be described by usinga flow chart shown in FIG. 12. The operation control of the rougheningroller 93 and the separation claw 34 with respect to the fixing roller40 is identical to that in Embodiment 1 (FIG. 10), so that the operationcontrol of the roughening roller 80 and the separation claw 35 withrespect to the pressing roller 41 will be described with reference toFIG. 12. First, in the case of performing a printout operation, the userinputs a transfer paper (recording material) condition and the number ofprintout copies to be made through the operation display portion B toset a printout condition. Then, the user turns on the copy start key(printout start switch) 400 to start the printout. When the printout isstarted, the controller A turns off a separation claw separationsolenoid 82 in the case where the basis weight of the recording materialS (the thickness of the paper) used for the sheet passing is not morethan 120 g/m² on the basis of the user input value to bring theseparation claw 35 into contact with the pressing roller 41 (YES of stepS1 and step S2).

Then, the controller A starts the sheet passing (step S3) to start theimage formation and also starts the fixing operation in the fixingdevice 13.

The controller A has a counting function for (integrally) counting thenumber of sheets of the recording material S subjected to the fixationin the state in which the separation claw 34 contacts the pressingroller 41. In the case where the sheet passing of 5000 sheets or more(integrated number of sheets) of the recording material is performed inthe contact state of the separation claw 35, the sheet passing job isinterrupted and the roughening operation (refreshing operation) of thepressing roller 41 by the roughening roller 80 is started by thecontroller A (step S4, YES of step S5, step S6, and step S7). Theroughening operation is performed under the above-described conditionfor the time period corresponding to 10 times of the rotation of thepressing roller 41 with respect to the roughening roller 80 in thisembodiment. The roughening roller 80 is configured to perform theroughening operation at regular intervals so as not to increase thesurface roughness non-uniformity of the fixing roller 40. When theroughening operation is completed, the sheet passing is resumed (step S2and step S3). When the printout on the set number of sheets is completedin accordance with the above-described routine, the sheet passing iscompleted (NO of step S5 and YES of step S10). When the sheet passing iscompleted, the separation claw separation solenoid 82 is turned on, sothat the separation claw 35 is moved away from the pressing roller 41(step S11).

In the step S1, in the case where the recording material to be fixed hasthe basis weight of more than 120 g/m² and in the case of the two-sideprinting mode (YES of step S8), the roughening operation of the pressingroller 41 by the roughening roller 80 is performed before the sheetpassing (step S9). This roughening operation is performed for a timeperiod corresponding to 10 times of the rotation of the pressing roller41 with respect to the roughening roller 80 in the state in which theseparation claw 35 is moved apart from the pressing roller 41.

Then, the controller A starts the sheet passing operation (step S10) toexecute the image formation operation and then completes the sheetpassing operation when the printout on the set number of sheets isended. In the case where the paper (recording material) to be fixed hasthe basis weight of not less than 120 g/m² and in the case of theone-side-printing mode, the separation claw 35 is in the separatedstate, so that the sheet passing is started as it is to effect the imageformation. When the printout on the set number of sheets is completed,the sheet passing is ended (step S11) and the solenoid is turned on(step S12).

By employing the above-described constitution, similarly as inEmbodiment 1, it is possible to obtain a good image even during theboth-side-printout.

As described above, the roughening operation of the fixing roller 40 isperformed in advance of the fixing operation when the toner images arefixed on the thin paper having the small basis weight and is notperformed in advance of the fixing operation when the toner images arefixed on the thick paper having the large basis weight. As a result, itwas possible to prevent the traces (of abrasion) from being transferredfrom the surface of the pressing roller 40 onto the toner images on thethin paper and to prolong the lifetime of the roughening roller 80.

Embodiment 3

As described above, when the recording material conveying speed isincreased, the surface transfer property is enhanced. In the state inwhich the surface transfer property is enhanced, the glossiness of thetoner images after the fixation is enhanced.

Further, in the case where the toner images are formed on both sides ofthe recording material, the glossiness of the toner images formed on therecording material surface after second passing of the recordingmaterial through the fixing nip is higher than that after first passingof the recording material through the fixing nip. This is because thetoner images formed on the recording material surface are heated againby the pressing roller 41 during the second passing of the recordingmaterial through the fixing nip. When the glossiness of the toner imagesis increased, the separation claw trace (by the separation claw 35) lefton the surface of the pressing roller 41 is more visible. Further, adifference in glossiness between the front-side toner images and therear-side toner images is also increased.

In the case where the toner images are formed on the both side surfacesof the recording material, the recording material passes through thefixing device 13 two times, so that there is no problem practically ifthe amount of heat to be applied to the toner images is decreased duringthe first passing of the recording material through the fixing nip sothat the toner images are fixed with reliability at the time ofcompletion of the second passing of the recording material.

Therefore, when the temperature on the pressing roller 41 side islowered and set at 150° C. during the two-sided printing (while thefixing roller 40 is kept at 180° C.), the separation claw trace left onthe surface of the pressing roller 41 is less visible, so that the tonerimage glossiness difference between the front surface and the rearsurface is also reduced. Further, a fixing property is also ensured, sothat a better image can be obtained.

As described above, due to the melting of only the transfer surface byhigh-speed printing, even when the transfer layer does not follow theuneven surface of the recording material but follows the surface of thefixing roller, the fixing roller surface is uniformly roughened by theabrading member (roughening member) during the passing of the recordingmaterial having a large basis weight (during the passing of the thickpaper). For that reason, the uneven glossiness on the image such as thesheet edge trace of abrasion or the separation claw trace is eliminated,so that it is possible to obtain a good image.

The separation claw is moved away from the fixing roller surface duringthe passing of thick paper and therefore the separation claw trace isnot left on the fixing roller surface also during the sheet passing, sothat there is no separation claw trace (no uneven glossiness) on theimage and therefore a good image can be obtained.

During the thin paper passing, the separation claw contacts the fixingroller, so that a separation performance can be kept at the same levelas that of a conventional device.

In the case of the plain paper, by bringing the separation claw intocontact with the fixing roller with a basis weight of not more than 120g/m² and by moving the separation claw away from the fixing roller withthe basis weight of more than 120 g/m², it is possible to retain thestate of a good separation performance with no image defect even whenthe paper with any basis weight is subjected to the fixation.

Even in the case where the separation claw is often brought into contactwith the fixing roller surface in such a state that the thin paper ispredominantly used as the recording material compared with the thickpaper, the fixing roller surface is made uniform by rougheningperiodically by the roughening member. Thus, when the fixing rollersurface is roughened by the roughening member, roughening non-uniformitydoes not occur and durability is of no problem.

Even in the case of the two-side sheet passing, the pressing rollersurface is uniformly roughened by the roughening member during thepassing of the thick paper, so that the uneven glossiness on the image,due to, for example, sheet edge trace of abrasion or the separation clawtrace can be eliminated to obtain a good image.

During the passing of the thick paper, the separation claw is moved awayfrom the pressing roller surface, so that the separation claw does notcontact the pressing roller surface even during sheet passing. For thatreason, even in the case of two-side sheet passing, the separation clawtrace (the uneven glossiness) on the image is eliminated, so that it ispossible to obtain a good image.

During thin paper passing, the separation claw contacts the pressingroller, so that the separation performance can be kept at a levelequivalent to that of the conventional device even in the case of thetwo-side sheet passing.

In the case of the plain paper, by bringing the separation claw intocontact with the pressing roller when the plain paper has a basis weightof not more than 120 g/m² and by moving the separation claw away fromthe pressing roller when the paper has a basis weight of more than 120g/m², it is possible to retain the state of a good separationperformance with no image defect even when paper with any basis weightis subjected to the fixation.

Even in the case where the separation claw is often brought into contactwith the pressing roller surface in such a state that the thin paper ispredominantly used as the recording material compared with the thickpaper, the pressing roller surface is kept uniform by rougheningperiodically by the roughening member. Thus, when the pressing rollersurface is roughened by the roughening member, the rougheningnon-uniformity does not occur and durability is not a problem.

In the case where the toner images are formed on two surfaces of therecording material, the temperature of the pressing roller 41 is loweredduring the second passing of the recording material through the fixingnip, so that it is possible to prevent toner image glossiness on thefront surface from excessively increasing compared with the toner imageglossiness on the rear surface. Therefore, the glossiness differencebetween the toner images on the front surface and the rear surface isreduced, so that a good image can be obtained.

The roughening roller as the abrading member abrades at least one of thefixing roller 40 and the pressing roller 41 as a pair of rotatablemembers. Further, the separating member separates the recording materialhaving passed through the heating nip from the rotatable member, whichis capable of being abraded by the abrading member.

The present invention is described above based on the specificembodiments but is not limited thereto. For example, the image heatingapparatus is not limited to the fixing device for fixing the unfixedtoner images, formed on the recording material, on the recordingmaterial. It is also possible to use the image heating apparatus as asmoothness-enhancing apparatus and a glossiness-enhancing apparatuswhich are used for increasing the smoothness and glossiness of the imageby heating the toner images again after the toner images are fixed onthe recording material, so that the same effect as that described abovecan be achieved.

Further, as the pair of rotatable members, such an embodiment that thefixing process is performed by the roller-like members, such as thefixing roller and the pressing roller. is described but the presentinvention is also applicable to even an apparatus (device) forperforming the fixing process by using belt-like members (a fixing beltand a pressing belt) as the pair of rotatable members.

While the invention has been described with reference to the structuresdisclosed herein, it is not confined to the details set forth and thisapplication is intended to cover such modifications or changes as maycome within the purpose of the improvements or the scope of thefollowing claims.

This application claims priority from Japanese Patent Application No.137768/2008 filed May 27, 2008, which is hereby incorporated byreference.

1. An image heating apparatus comprising: a heating member configured toheat a toner image on a recording material in a heating nip; a pressingmember configured to form the heating nip and being in contact with saidheating member; an abrading member configured to abrade a surface ofsaid pressing member; contact-and-separation means for causing contactand separation of said abrading member with respect to said pressingmember; and selecting means for selecting, depending on the basis weightof the recording material to be heated by said heating member, whetheror not said contact-and-separation means brings said abrading memberinto contact with said pressing member before the recording material isconveyed to the heating nip.
 2. An apparatus according to claim 1,wherein said selecting means causes said contact-and-separation means tobring said abrading member into contact with said pressing member whenthe basis weight of the recording material is more than a predeterminedamount.
 3. An apparatus according to claim 2, wherein said abradingmember has a surface roughness R2 of 3 μm to 16 μm at a surface on whichsaid abrading member contacts said pressing member.
 4. An apparatusaccording to claim 3, further comprising a separating member configuredto separate the recording material, which has passed through the heatingnip, from said heating member, wherein said contact-and-separation meansmoves apart from a separation position, for permitting separation of therecording material from said pressing member, before said contact andseparation means brings said abrading member into contact with saidpressing member.
 5. An apparatus according to claim 4, wherein saidseparation member is located at the separation position during passingof the recording material through the heating nip when the basis weightof the recording material is less than the predetermined amount.